1. Field of the Invention
The present invention relates to a mobile communication system and, more particularly, to a method for selecting a ciphering process when a radio resource control layer designates a radio bearer.
2. Description of the Related Art
In the 3rd generation partnership project (3GPP), which is a third generation network and radio access system, the radio resource control (RRC) layer is a protocol layer that controls each layer. The RRC layer belongs to the third layer out of 3 lower layers of the open systems interconnection (OSI) reference model. The three lower layers include a packet data convergence protocol (PDCP) layer, a broadcast/multicast control (BMC) layer, a radio link control (RLC) layer, a medium access control (MAC) layer, and a physical (PHY) layer. Here, the PHY layer belongs to the first layer, and the other layers, that is, the PDCP layer, BMC layer, RLC layer and MAC layer belong to the second layer.
FIG. 1 is a schematic diagram illustrating a configuration of the radio interface protocol in the 3GPP. The radio interface protocol includes an RRC layer 10 that controls each layer, a PDCP layer 21 that transfers packet data, a BMC layer 22 that transfers broadcast and multicast data, an RLC layer 23 that is in charge of flow control as a data link layer, a MAC layer 24 that transfers (or bears) the data provided by RLC layer 23, using an appropriate mapping relation between a logical channel and a transport channel, and a PHY layer 30 that transfers data to a radio section by loading the data into a physical channel.
The RRC layer 10 is defined on a control plane only and is in charge of controlling the transport channels and the physical channels, in connection with setup, reset, and release of radio bearers (RB). To set up the radio bearers means to define protocol layers and channel characteristics necessary to provide a specific service and to designate each concrete parameter and operation method.
PDCP 21 is located at an upper portion of the RLC layer and makes the data, which has been transmitted through a network protocol like IPv4 or IPv6, transmittable through an air interface.
BMC layer 22 transfers a message from a cell broadcast center (CBC) through the air interface. More specifically, BMC layer 22 schedules a cell broadcast message, which has been transferred through an end, before actually transferring the message. In general, BMC layer 22 transfers the data through RLC layer 23, which is operated in an unacknowledged mode (UM).
RLC layer 23 configures an appropriate RLC protocol data unit (PDU) for transfer, to achieve a better segmentation and concatenation feature for the RLC service data unit (SDU) that is transferred from a higher layer. RLC layer 23 performs an automatic repeat request function (ARQ) that is responsible for retransmission of an RLC PDU lost during transfer. Based on how the RLC PDU is transmitted from a higher layer, PLC layer 23 operation may be characterized as transparent mode (TM), acknowledged mode (AM), and unacknowledged mode (UM). RLC layer 23 has an RLC buffer for storing the RLC SDU or RLC PDU.
A logical channel (L_CH: Logical CHannel) is interposed between and accessed by RLC layer 23 and MAC layer 24. To perform frequency division duplex (FDD), the current 3GPP uses 6 logical channels, including DTCH, DCCH, CTCH, CCCH, BCCH and PCCH.
The Dedicated Traffic CHannel (DTCH) is a channel that transfers dedicated data of a specific user equipment (UE), and the Dedicated Control CHannel (DCCH) is a channel that transfers dedicated control information of a specific user equipment. The Common Traffic CHannel (CTCH) is a channel that transfers common data to a number of user equipments, and the Common Control CHannel (CCCH) is a channel that transfers common control information to a number of user equipments. Also, the Broadcast Control CHannel (BCCH) is a channel that transfers broadcast information, and the Paging Control CHannel (PCCH) is a channel that transfers paging information.
The transport channel (T_CH: Transport CHannel) is interposed between and accessed by MAC layer 24 and PHY layer 30. In this case, 7 transport channels, including DCH, BCH, FACH, PCH, RACH, CPCH and DSCH, are used to support FDD.
First of all, the Dedicated CHannel (DCH) is a channel for transferring dedicated data of a specific user equipment, and the Broadcast CHannel (BCH) is a channel for transferring broadcast information. The Forward Access CHannel (FACH) is a channel for transferring forward (down) data, and the Paging CHannel (PCH) is a channel for transferring paging information. The Random Access CHannel (RACH) is a channel for transferring reverse data, the Common Packet CHannel (CPCH) is a channel for transferring small packet data, and the Downlink Shared CHannel (DSCH) is a channel for transferring a large volume of data in a forward direction.
A plurality of logical channels (L_CH) can be multiplexed to make one transport channel (T_CH). Similarly, a plurality of transport channels (T_CH) can be multiplexed to make one physical channel.
Using the configuration described above and illustrated by FIG. 2, the radio interface protocol performs a radio bearer (RB) setup process for defining or specifying characteristics of layers and channels necessary to provide a specific service. This radio bearer setup process is depicted in FIG. 2.
Particularly, FIG. 2 illustrates the method for setting up a radio bearer in the radio interface protocol of the related art. To set up the RB, RRC layer 204 first receives a radio bearer setup command from one or every layer, including a peer RRC 201, a higher layer 202 and a BMC layer 203, respectively (S211 through S213). Then, RRC layer 204 transfers the radio bearer setup command to lower layers (e.g., BMC layer 203, PDCP layer 205, RLC layer 206, MAC layer 207, or PHY layer 208) to set up an appropriate layer for data service (S221 through S225). Therefore, through the radio bearer setup process, it is decided whether or not to use PDCP layer 205 and BMC layer 203. Also, it is decided as to which one of several RLC modes, particularly among the acknowledge mode (AM), unacknowledged mode (UM), or transparent mode (TM), should be used. Moreover, while generating an RLC entity, it is decided which logical channel should be used in between RLC layer 206 and MAC layer 207, and which physical channel should be used in PHY layer 208. In short, a radio bearer is set up by specifying the parameters and the operation method thereof.
RLC layer 206, unlike the other layers, is not always available. In fact, it is generated only when the RB is setup and discarded after providing a service.
According to the current 3GPP standard, one RB must use one RLC entity. Also, a user equipment can accommodate a maximum of 32 radio bearers at one time, and unlike the other layers, a number of RLC entities can exist at the same time.
The RLC entity is divided into a transparent mode (TM) entity, to which an RLC header is not attachable, and a non-transparent mode entity, to which an RLC header is attachable. The non-transparent mode entity can be further divided into the acknowledge mode (AM) entity, having an acknowledge signal, and the unacknowledged mode (UM) entity that lacks an acknowledge signal.
Configuration of the RLC AM entity will now be explained with reference to FIG. 3. As shown in the drawing, the AM entity 320 at the transmitting side carries out a segmentation/concatenation process 301 to produce uniformly sized protocol data units, from the service data units received from a higher layer. Thereafter, a header having a sequence number (SN) is integrated 302 into the protocol data unit.
The PDU, including the header, is saved in a retransmission buffer 303, in case it needs to be retransmitted later. In the meantime, this PDU is multiplexed by a multiplexer 304 and is ciphered 305 for the sake of data security.
Afterwards, the ciphered PDU is temporarily stored in the transmission buffer 306 and is transferred to a set fields block 307. With set fields block 307, other fields (e.g., D/C and Poll field), except for the sequence number of the RLC header, are set to appropriate values and transferred to a lower layer.
The PDU loaded with data information from a higher layer is called an AM Data (AMD) PDU and the configuration thereof is shown in FIG. 4. As depicted in the drawing, the RLC layer includes two kinds of protocol data units with different formats. One of them is an Unacknowledged Data PDU (UMD PDU), which is used especially when no acknowledge signal needs to be sent to the transmitting side. The other is an Acknowledged Data PDU (AMD PDU), which is used when an acknowledge signal does need to be sent to the transmitting side. As shown in FIG. 4, AMD PDU includes a header, a length indicator group, data, and padding (PAD) or a piggyback type of PDU.
Ciphering is performed on the AMD PDU only. The header group, particularly the first two octets (a group including sequence number), is not enciphered, only the groups after the header group are enciphered.
The receiving side of AM entity 320 demultiplexes 308 the protocol data units transferred from a lower layer and stores the demultiplexed protocol data units in the receiving buffer 309, temporarily. Once all of the protocol data units needed to configure a complete SDU are received, AM entity 320 deciphers 310 these protocol data units, removes 311 the RLC header, reassembles 312 the deciphered protocol data units into the SDU, and transfers them to a higher layer.
FIG. 5 illustrates an RLC UM entity 500. The transmitting side 501 UM entity 500 performs the segmentation/concatenation process 503, to form the service data units received from a higher layer into uniformly sized PDUs, and enciphers 504 the PDU for the sake of data security. Later, RLC UM entity 500 configures UMD protocol data units by including 505 the header, having a sequence number, storing the UMD protocol data units in the transmission buffer 506, and transferring the UMD PDUs to the radio section through a lower layer.
FIG. 6 shows the configuration of the UMD PDU. Referring to FIG. 6, the UMD PDU includes a header, a length indicator group, data, and a PAD. The first octet in the UMD PDU format indicates a header having a sequence number. This header group is not enciphered, but the rest of the group is enciphered.
Referring again to FIG. 5, the receiving side 502 of UM entity 500 receives the UMD PDU and stores it in the receiving buffer 507, temporarily. When all of the protocol data units needed to configure a complete SDU are received, the RLC header is removed 508 from the protocol data units. Then, UM entity 500 deciphers 509 the protocol data units, reassembles 510 the deciphered protocol data units into the SDUs, and finally transfers the SDUs to a higher layer.
The 3GPP system conducts the ciphering process to secure user data. The ciphering process is carried out in the RLC layer, according to the RLC mode, especially when the AM and UM are involved. On the other hand, ciphering is performed in the MAC layer when the TM is involved. One thing to notice here is that not all data is enciphered. That is to say, in case of the AM and UM, the ciphering process is performed only on the data that is transferred to the DTCH or DCCH logical channels and not for the other logical channels. And, in case of the TM, only the data transferred to the DCH transport channel, but not the other transport channels, goes through the ciphering process. This ciphering process is not available for every radio bearer though. Instead, it is decided whether or not to carry out the ciphering process on all of the radio bearers overall.
In general, when the enciphered data is transferred to the receiving side from the transmitting side, the receiving side reconstitutes the data through the deciphering process. At this time, it is important that the transmitting side and the receiving side use the same algorithm and ciphered parameters in order to transceive data more precisely. This may be better understood with reference to FIGS. 3 and 5.
However, one problem of the traditional method is that the ciphering process can′t be separately performed on an individual radio bearer, since the ciphering process is performed on all of the radio bearers or none at all. In other words, if the user wishes to carry out the ciphering process on a certain radio bearer only, while leaving other radio bearers alone, the related art method for setting up the radio bearer is certainly not the right choice.
For example, the BMC data currently uses the RLC UM entity and is transferred to the CTCH, among other logical channels. Therefore, no ciphering process is performed on the BMC data. The problem with this is that within the BMC data there is data that does not have to be enciphered, but also data that does need to be enciphered. Thus, the ciphering process has to be performed on the radio bearers selectively. For example, the BMC service includes Short Message Service—Cell Broadcast (SMS-CB), Short Message Service—Point to Point (SMS-PP), IP multicast service and so forth. SMS-CB service has the information for all user equipment in a cell, so there is no need to carry out the ciphering process.
By contrast, as far as the SMS-PP service is concerned, because one specific user equipment has a message only for another specific user equipment, the ciphering process is needed. Similarly, for IP multicast service, the information should be transferred to a user equipment in a particular group, so again the ciphering process needs to be done. However, according to the previous method for setting up the radio bearer, when the SMS-PP service or the IP multicast service are concerned, there were only two options for the equipments, that is, whether they are collectively enciphered or not. Therefore, discrimination of the ciphering service was impossible, and the SMS-CB service and the SMS-PP service could not be performed simultaneously no matter what.
Besides, if one provides a specific service, while ciphering the service at the same time, and then decides not to encipher the service at a certain point, the traditional method for setting up the radio bearer simply could not change the ciphering on that specific radio bearer, but instead all radio bearers had to be reset from the beginning. Furthermore, the information about every layer must be recollected to set up all of the radio bearers, and while doing so, a number of signaling overheads are caused. Even worse, a great amount of time is wasted in deciding whether or not to encipher the specific radio bearer.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.